Project Summary/Abstract: Many in vitro studies, post-mortem brain studies, and proteomic studies in plasma and cerebral spinal fluid have described the presence of increased immune activation in ASD, whilst clinical and epidemiological studies suggest that there is an increase in immune mediated conditions such as atopy and autoimmunity. Activation of these immune responses is more prominent in individuals with exacerbated behavioral impairments in ASD. Despite recent advances, there is a large gap in our knowledge regarding pathophysiological pathways in ASD. We hypothesize that an underlying mechanism common to this diverse array of findings is the lack of immune control or regulation that can lead to immune activation and inflammation. Regulatory T cells (Tregs) are key mediators of immune tolerance that maintain their lineage commitment and function through epigenetic regulation, and restrain inappropriate inflammation. We and others have previously demonstrated decreased frequencies of Tregs-and immunosuppressive cytokines including transforming growth factor (TGF)?1 and interleukin (IL)-10.Our new preliminary data shows that these immune regulatory deficits are associated with more severe behavioral phenotypes. However, no studies have yet to address the functional cellular mechanisms of Tregs in ASD. We will test the innovative hypothesis that a lack of cellular immune regulation is an early predictive risk factor for ASD, and that it endures in children with ASD who have received a diagnosis. Considering that impairments in social interaction and anxiety are key features of ASD, the amygdala has been extensively implicated in ASD pathophysiology. We will also address the absence of immune regulation in the amygdala of individuals with ASD and matched controls over development. This is an important area of investigation since therapeutic targeting of immune control mechanisms might improve immune function, address abnormal amygdala development and alleviate behavioral abnormalities. The proposed studies will determine immune regulation, Treg cellular function and epigenetic mechanisms controlling Tregs commitment and stability (Aim #1) in children with ASD and typically developing (TD) controls. In two prospective, population based cohorts we will examine immune regulatory mechanisms in cord blood samples from children that later receive a diagnosis of ASD, or TD (Aim #2). The proposal will directly assess the relationship of predictive and longitudinal measures of immune dysregulation and behavior abnormalities in ASD. We will examine amygdala growth over development into adulthood and immune regulation in human samples from ASD and TD controls (Aim #3). If successful, this research will validate the transformative concept that ASD is, for some, a disorder due to defects in immune regulation and will validate a novel mechanism for one of the most visible public health concerns of our time. .